Make deb package repository for Tor/Mullvad Browser

In order to have a package repository for Tor/Mullvad Browser deb package (done in #41083 (closed)), I'm thinking about doing the following:

during the build:

after creating the deb package, use reprepro to create a simple repository containing only the {mullvad,tor}-browser package, and make a tarball of the repository (excluding the pool directory which contains the package).

during signing/publishing (in tools/signing):

extract the deb repository and sign the file ./dists/{mullvad,tor}-browser{,-alpha}/Release using our gpg key.
update tools/signing/upload-update_responses-to-staticiforme to copy the deb repository and the Release.gpg file to a deb directory in {mullvad,tor}-browser-update-responses.git, and commit/push.
update tools/signing/staticiforme-prepare-cdn-dist-upload to copy the .deb file with the .mar files to /srv/cdn-master.torproject.org (for Tor Browser only).
in tor-browser-update-responses.git, add a redirect from ./pool/main/t/tor-browser{,-alpha} to https://cdn.torproject.org/aus1/torbrowser/$version.
in mullvad-browser-update-responses.git, add a redirect from ./pool/main/m/mullvad-browser{,-alpha} to https://cdn.mullvad.net/browser/$version.
then when we run deploy_update_responses-{alpha|release}.sh on staticiforme (for Tor Browser), it will deploy the updated deb repository at the same time as enabling the update in the internal updater.

I think the lines to add in /etc/apt/sources.list would be something like this:

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